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[RC] Heart size - Ridecamp Guest

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Authors LE Young, K Rogers, JLN Wood
Title   Left ventricular size and systolic function in Thoroughbred racehorses 
and their relationships to race performance
Full source     Journal of Applied Physiology, 2005, Vol 99, Iss 4, pp 1278-1285

Cardiac morphology in human athletes is known to differ, depending on the 
sports-specific endurance component of their events, whereas anecdotes abound 
about superlative athletes with large hearts. As the heart determines stroke 
volume and maximum 02 uptake in mammals, we undertook a study to test the 
hypothesis that the morphology of the equine heart would differ between trained 
horses, depending on race type, and that left ventricular size would be 
greatest in elite performers. Echocardiography was performed in 482 race-fit 
Thoroughbreds engaged in either flat (1,000-2,500 in) or jump racing 
(3,200-6,400 in). Body weight and sex-adjusted measures of left ventricular 
size were largest in horses engaged in jump racing over fixed fences, compared 
with horses running shorter distances on the flat (range 8-16%). The observed 
differences in cardiac morphologies suggest that subtle differences in training 
and competition result in cardiac adaptations that are appropriate to the 
endurance component of the horses' event. Derived left ventricular mass was 
strongly associated with published rating (quality) in horses racing over 
longer distances in jump races (P <= 0.001), but less so for horses in flat 
races. Rather, left ventricular ejection fraction and left ventricular mass 
combined were positively associated with race rating in older flat racehorses 
running over sprint (< 1,408 in) and longer distances (> 1,408 in), explaining 
25-35% of overall variation in performance, as well as being closely associated 
with performance in longer races over jumps (23%). These data provide the first 
direct evidence that cardiac size influences athletic performance in a group of 
mammalian running athletes.


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